5,6-dimethylxanthenone-4-acetic acid (DMXAA) is represented by the following formula:

Phase I clinical trials of DMXAA have recently been completed, with dynamic MRI (Magnetic Resonance Imaging) showing that it induces a significant reduction in tumour blood flow at well-tolerated doses. DMXAA is thus one of the first antivascular agents for which activity (irreversible inhibition of tumour blood flow) has been documented in human tumours. These findings are in agreement with preclinical studies using tumours or human tumour xenografts which showed that its antivascular activity produced prolonged inhibition of tumour blood flow leading to extensive regions of haemorrhagic necrosis. However, in such studies tumours rapidly regrow from surviving cells in the well-perfused periphery. The transient tumour growth inhibition seen in most preclinical models is consistent with the lack of tumour regressions seen in the phase I clinical studies, and suggests that DMXAA is unlikely to have clinical utility as a single agent.